1. Field of the Invention
The present invention relates to a printing apparatus and ink discharge failure detection method. Particularly, the present invention relates to a printing apparatus which prints by causing film boiling in ink by an electrothermal transducer and discharging ink by the bubbling force, and an ink discharge failure detection method.
2. Description of the Related Art
An inkjet printing apparatus (to be referred to as a printing apparatus hereinafter) prints various kinds of information by discharging ink from the discharge orifices of a printhead onto a printing medium such as paper. This printing apparatus has many advantages such as noise reduction, high-speed printing, and a wide selection of printing media. A type of printhead in which thermal energy acts on ink to discharge ink from the discharge orifices can quickly respond to a printing signal and easily increase both the number of discharge orifices and their integration density.
In a printing apparatus using such a printhead, a discharge failure occurs in the entire printhead or some discharge nozzles due to clogging of a discharge orifice with a foreign substance, bubbles trapped in the ink supply channel, and/or change of the wet condition of the nozzle surface. A discharge failure may also occur owing to disconnection of an electrothermal transducer (heater) or the like upon long-term use.
A full-line printing apparatus in which a number of printing elements are linearly arrayed, corresponding to the overall width of a printing medium can print at high speed. However, it is a key issue to identify a discharge nozzle suffering a discharge failure at high speed and reflect the identification result in image complement and the printhead recovery procedure. A printing apparatus using such a printhead may impair the image stability owing to change of the ink discharge amount upon temperature change of the printhead. Especially, it is very important for the full-line printing apparatus to obtain a high-quality image by suppressing image deterioration upon change of the ink discharge amount.
In consideration of the above importance, there have conventionally been proposed various ink discharge failure detection methods, ink discharge failure complement methods, discharge amount control methods, and apparatuses adopting these methods.
For example, Japanese Patent Laid-Open No. 6-079956 discloses a configuration of detecting a printed image to obtain a faultless image. For this purpose, a predetermined pattern is printed on a detection sheet and read by a reader to detect an abnormal printing element. Japanese Patent Laid-Open No. 6-079956 also discloses a configuration of moving image data assigned to an abnormal printing element, superposing it on image data assigned to another printing element, and thereby complementing printing.
Japanese Patent Laid-Open No. 3-234636 discloses a configuration of making ink discharge states from a full-line inkjet printhead uniform. This configuration employs a detection feature (read head) serving as a photosensor (e.g., an amorphous silicon hydride sensor or CCD), and a setting feature. The detection feature detects whether or not ink was discharged, and the setting feature sets the head on the basis of driving conditions when the detection feature detects ink discharge.
As a method of detecting discharging of ink droplets, Japanese Patent Laid-Open No. 2-194967 discloses a configuration of determining the printing liquid discharge state of each discharge orifice by using a feature for detecting a discharged printing liquid. In this configuration, pairs of light-emitting elements and light-receiving elements are arranged near the two ends of the discharge orifice array of a printhead. Japanese Patent Laid-Open No. 58-118267 discloses a method of detecting an ink discharge state at an ink discharge source. According to this method, conductors are arrayed at positions where the resistance value changes due to heat generated by electrothermal transducers. The change amount of the resistance value depending on the temperature of each conductor is detected, and applying a discharge signal to the electrothermal transducer stops in accordance with the temperature change.
Japanese Patent Laid-Open No. 2-289354 discloses a configuration of detecting ink droplets at the discharge source. For this purpose, electrothermal transducers and temperature sensors are formed on the same base such as a Si substrate, and the film temperature sensors overlap the array area of the electrothermal transducers. Japanese Patent Laid-Open No. 2-289354 also discloses a configuration of determining a discharge failure from change of the resistance value of the temperature sensor depending on temperature change. Further, Japanese Patent Laid-Open No. 2-289354 further discloses a configuration in which film temperature sensors are formed on a heater board by the film forming process, and connected to the outside via terminals by a method such as wire bonding.
However, the method disclosed in Japanese Patent Laid-Open No. 6-079956 cannot detect a discharge failure at high response speed. Moreover, it requires paper for test printing and a reader, raising the apparatus cost and running cost.
In the apparatus disclosed in Japanese Patent Laid-Open No. 3-234636, the detection feature serving as a photosensor (e.g., an amorphous silicon hydride sensor or CCD) must be arranged outside the printhead. The printing apparatus disclosed in Japanese Patent Laid-Open No. 2-194967 requires pairs of light-emitting elements and printing elements arranged near the two ends of the discharge orifice array of a printhead. For this reason, these two prior arts can hardly reduce the apparatus size and cost.
Furthermore, Japanese Patent Laid-Open No. 58-118267 does not explicitly disclose a detection circuit which detects an optimal position where the resistance value changes due to heat generated from an electrothermal transducer, and detects the change amount of the resistance value that depends on the temperature of each conductor. Hence, a specific configuration of identifying a nozzle suffering a discharge failure at high speed is unknown. At a position adjacent to an electrothermal transducer disclosed in this conventional art, it is difficult to detect a nozzle suffering a discharge failure at high speed. This will be described in detail later.
In the printhead disclosed in Japanese Patent Laid-Open No. 2-289354, electrothermal transducers and temperature sensors are formed on the same base such as a Si substrate, and the film temperature sensors overlap the array area of the electrothermal transducers. Thus, a discharge failure is detectable at high speed, but the position of each faulty nozzle cannot be identified.
In the configuration disclosed in Japanese Patent Laid-Open No. 2-289354, the memory stores an enormous amount of resistance value data because all resistance values are stored at each heating time regardless of the presence/absence of heating data. In the analysis, all the resistance value data must be checked to identify heated nozzles from the presence/absence of temperature rise. Then, discharge failure determination starts. If the temperature does not rise, “no heating data” is determined. Even in the presence of heating data, however, if the heater fails due to disconnection or the like, “no heating data” is also determined, and “heater failure” cannot be identified.